The Trade Calculator App Electricians Will Actually Pay For

Here’s a category of software buyer most indie developers never think about: the electrician standing in a crawl space at 7am trying to figure out what wire gauge he needs for a 60-amp subpanel run of 110 feet. He’s not browsing Product Hunt. He’s not reading software as a service (SaaS) newsletters. But he has a phone in his pocket, a real problem in front of him, and a company card that will happily cover a $40-a-year app if it saves him ten minutes on every job.

This idea has shown up four times in the opportunity data we track, cracked the top 15 three of those times, and peaked at #8. That’s a strong signal for something this unglamorous. The pitch: a polished calculator suite plus a searchable code-reference tool for skilled trades, sold as a pro app at $30-60 per year. Electricians, plumbers, and HVAC techs are the obvious first markets.

The problem is real and the competition is genuinely bad

Go search the App Store for “wire size calculator” or “voltage drop calculator” right now. What you’ll find is a graveyard. Apps last updated in 2019. Interfaces that look like they were built for the original iPhone. Free calculators stuffed with banner ads that cover the input fields. Reviews full of pros saying the same thing: “This would be great if it didn’t crash” or “I’d pay to remove the ads and get National Electrical Code (NEC) 2023 tables.”

That last part matters. In most app categories, complaints about ads mean nothing because nobody actually pays. Trades are different. These are people who spend $300 on a Klein multimeter and $80 on a paper code book that goes out of date every three years. A digital tool that’s accurate, fast, and works offline in a basement isn’t an impulse buy for them. It’s equipment. And equipment gets paid for without much agonizing.

What you’d actually build

The core product is two things bolted together. First, a calculator suite: wire sizing, voltage drop, conduit fill, box fill, load calculations for services and feeders, motor calculations. For plumbers it’s pipe sizing, fixture unit counts, and slope. For heating, ventilation, and air conditioning (HVAC) it’s duct sizing, refrigerant charge, and cubic feet per minute (CFM) math. Each trade has maybe eight to fifteen calculations that come up constantly, and pros know exactly which ones they are.

Second, a searchable reference layer. Not the full code text, which is copyrighted and licensed, but the derived tables and rules of thumb that pros look up daily: ampacity tables, bend radius requirements, clearance rules, common inspection triggers. You can build this from publicly available derived data and your own explanatory content, the same way a hundred study-guide publishers do. If the app takes off, licensing actual code content from the National Fire Protection Association (NFPA) or the International Code Council (ICC) becomes a real conversation, but you don’t need it on day one.

The build itself is not technically hard. This is forms, math, and lookup tables. No artificial intelligence (AI) infrastructure, no real-time anything, no scaling problems. A competent developer, or a determined founder working with modern coding tools, can ship a credible v1 in two to three months. The hard part isn’t code. It’s getting the numbers right, because a wrong wire-sizing answer isn’t a bug, it’s a fire hazard and a lawsuit. Budget real money and time for a licensed electrician or master plumber to review every formula and table. That review is your moat as much as your liability shield.

Distribution is the App Store, and that’s a feature here

Normally we’re skeptical when a business plan says “people will just find us in the App Store.” For most consumer apps that’s wishful thinking. But trades apps are one of the few categories where search-driven discovery genuinely works, because the intent is so specific. Nobody types “conduit fill calculator” into an app store casually. Every single person searching that phrase is your customer, and the incumbents ranking for it are weak.

Layer on the word-of-mouth dynamics of a jobsite. Trades work happens in crews. When the journeyman pulls out an app that answers a question in fifteen seconds while the apprentice is still flipping through a code book, that app gets installed on three more phones by lunch. Apprentices studying for licensing exams are another quiet channel; exam prep is exactly the kind of use case that turns into an annual subscription that never gets cancelled.

The retention story is what we’d call “lives in the work truck” stickiness. This isn’t an app someone opens twice and forgets. It’s used daily, on the clock, for money-making work. Annual churn on tools like this tends to be far lower than typical consumer subscriptions, because cancelling means going back to a worse workflow that costs real time.

The money, honestly

At $40 a year, a thousand subscribers is $40,000 in annual revenue, minus Apple and Google’s cut, so call it $34,000. That’s a solid side business, not a rocket ship. Getting to 5,000 subscribers across two or three trades puts you around $170,000 net, which is a real company for one or two people. There are over 700,000 electricians in the US alone, plus roughly comparable plumber and HVAC populations, so 5,000 paying users is a fraction of one percent penetration. The ceiling isn’t the market. It’s how well you execute and how long you stick with it.

The honest caveats. Code references change on a three-year cycle and vary by state and local jurisdiction, so this is a living product with permanent maintenance obligations, not a build-once asset. Liability is real; you need clear disclaimers, professional review, and probably an LLC and insurance before you charge a dime. Apple’s review process and 15-30% cut are the cost of the distribution channel. And a well-funded incumbent like a tool manufacturer could decide to give a decent version away as marketing, though they’ve had two decades to do that well and mostly haven’t.

Who this isn’t for

Skip this one if you have zero connection to the trades and no willingness to build one. The product decisions here, which calculations matter, what inputs pros actually have on hand, what a code inspector flags, all come from domain knowledge you can’t fake. If you can’t spend time with working electricians or hire one as an advisor, you’ll build a technically correct app that feels wrong in the field. It’s also a bad fit if you want fast money; app subscriptions compound slowly, and year one might net you a few thousand dollars while reviews and rankings build.

But if you’re a developer with a family member in the trades, or a former tradesperson who learned to code, this is close to an ideal match: a paying audience with bad tools, searchable intent, daily use, and competitors who stopped trying years ago. We’ll be honest, most app ideas we look at fail on distribution. This one fails only on execution, and that part is up to you.